That is, you need a balun. There has been a lot of talk about baluns here and at other forums.
These stop or attenuate RF in the shack and make VNAs work
I have used Digikey. Mouser and others are good too, ofcourse. These are what Digikey has. The idea is to get a high impedance between antenna and feedline.
Take highest impedance at your frequency and what has large enough diameter for your cable.
|
Use a small common mode choke at the antenna to decouple your body parts from the measurements. *Clyde K. Spencer* On Tue, May 27, 2025 at 4:30?PM Jim K4JDH via groups.io <k4jdh= [email protected]> wrote: I could but that would require a coax jumper of sufficient length to avoid
de-tuning by my body. As is, the jumper goes from the radio to the attic,
maybe 30 feet in length. After adjustments are made I simply step away 10
feet and look at my phone.
As I said, my main concern was overall system SWR so as not to cook my
radio. If the antenna performs, I am good with it. So far it seems to do
OK. Also, this is Alabama in May. The less time spent in a hot attic the
better. Thanks.
|
I could but that would require a coax jumper of sufficient length to avoid de-tuning by my body. As is, the jumper goes from the radio to the attic, maybe 30 feet in length. After adjustments are made I simply step away 10 feet and look at my phone.
As I said, my main concern was overall system SWR so as not to cook my radio. If the antenna performs, I am good with it. So far it seems to do OK. Also, this is Alabama in May. The less time spent in a hot attic the better. Thanks.
|
You should not need a THRU or ISOLATION calibration for a pure S11 measurement though it doesn't hurt. Many beginners forget to tap DONE when they are finished with their SOL calibration...
|
you try everything and nothing works.
This is why being able to have an onsite nanoVNA measure at the antenna may be the only definitive answer.
The nanoVNA does not lie BUT you must ensure ALL the Calibrations are spot on.
I had a case recently where the trace was jumping all around and no matter what I did I could not get a proper reading.
Until I remembered, the THRU path was not calibrated. there are cases when the other port is seeing something, and ensuring the thru (port to port) is calibrated the device will only tell you what it is seeing and if you have NOT calibrated out ALL the extraneous anomalies your measurement will be compromised.
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Why not tune right at the antenna in the attic using the NanoVNA?
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Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
Well I have a varied Career in Broadcasting from floor Technician to RF Engineer in Transmitters, AM, FM and TV 5 Watt relays to 50 KW base stations.
Then I went on to Telus a Telcom was involved it cellular Antennas and RF Systems.professionally the VNA was indispensable. Now in Amateur radio it is an affordable tool giving incredible results.
I may have to invest in a Tiny SA next. Chip technology has made so many thing almost common place.
Enjoy your retirement I know I am. 73 Dave VE6LX
|
Jim, others may have done this but I haven¡¯t seen their posts. What a great idea!
KI4QCK
toggle quoted message
Show quoted text
On May 26, 2025, at 11:36?AM, Jim K4JDH via groups.io <k4jdh@...> wrote:
?Surely I am not the first to do this but I want to crow anyhow.
I have just setup a 6M Yagi in my attic. I am mostly concerned with overall system SWR. I put the VNA at the shack end along with a webcam. What a joy this was to tune. When I did this a few years ago I traveled the stairs way too many times. I also have an 80-10 EFHW that may benefit from this in the fall.
|
Surely I am not the first to do this but I want to crow anyhow.
I have just setup a 6M Yagi in my attic. I am mostly concerned with overall system SWR. I put the VNA at the shack end along with a webcam. What a joy this was to tune. When I did this a few years ago I traveled the stairs way too many times. I also have an 80-10 EFHW that may benefit from this in the fall.
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Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
Thank you Dave for your experimentation with this little VNA wonderbox. I am discovering what it can do. So far it has enabled me to avoid frustrations with some uhf antennas I am playing with. Retirement is indeed busier than when I was employed in the Bell System.
--
73 de W8NSI Jim
New NanoVNA User, please be patient.
I build my own antennas and need this.
When Tyranny becomes Law, Revolution becomes Duty!
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Re: Microwave Journal ... RF Engineering Education at University of Bristol
On Wednesday 21 May 2025 05:09:45 pm alan victor via groups.io wrote: From Microwave Journal May 2025. An very nice article addressing RF Microwave Design and Measurments
at the University of Bristol. A series of You Tube Videos located on the reference page, at the
end of the paper, are well worth the time to highlight (copy) and watch including building a homemade
cal kit, copper tape microstrip and more.
The PAPER:
A YOU TUBE VIDEO on cal kits and their construction and more...
youtube.com/watch?v=Ws1mIK-JIrg That video led me to another one which finally landed me on this one: That guy does some pretty interesting stuff... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
But in retirement the work IS play! My 8753C weighs nearly 100 lbs.! No way is it going to accompany me outside to make measurements of antennas. The NANOVNA certainly can and does go outside to make measurements. Further, the 8753C can not make direct measurements of my long doublet fed with open wire line as it is connected to the power grid and house wiring. The NANOVNA is small enough to make those measurements in the shack with nothing between it and the NANO. I just hope and pray that it will continue to be available to amateurs, professionals, and the schools in the future. It's indispensable for anything associated with RF! Dave - W?LEV <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Wed, May 21, 2025 at 5:11?PM VE6LX via groups.io <dclarke2= [email protected]> wrote: I see another person who asks themselves where did I ever find time to
work. Retirement while every day "may" seem like Saturday there are days
when it feels more like the first day after after a long weekend and the
work is piled so high you can not see any daylight.
"The Golden Years, more like "Fools Gold" at times. "More Work and No Pay."
-- *Dave - W?LEV* -- Dave - W?LEV
|
Re: Microwave Journal ... RF Engineering Education at University of Bristol
You are welcome.
Since R&S was a partner in this education process, there are additional videos on more basic vna topics.
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Re: Microwave Journal ... RF Engineering Education at University of Bristol
Thanks a lot Alan for sharing this article. Skimmed through it and bookmarked for detailed reading. 73 Jon, VU2JO On Thu, May 22, 2025 at 2:39?AM alan victor via groups.io <avictor73= [email protected]> wrote: From Microwave Journal May 2025. An very nice article addressing RF
Microwave Design and Measurments
at the University of Bristol. A series of You Tube Videos located on the
reference page, at the
end of the paper, are well worth the time to highlight (copy) and watch
including building a homemade
cal kit, copper tape microstrip and more.
The PAPER:
A YOU TUBE VIDEO on cal kits and their construction and more...
youtube.com/watch?v=Ws1mIK-JIrg
|
Re: Jittery , non steady readings
Same thing happens at the countryside
|
Microwave Journal ... RF Engineering Education at University of Bristol
From Microwave Journal May 2025. An very nice article addressing RF Microwave Design and Measurments
at the University of Bristol. A series of You Tube Videos located on the reference page, at the
end of the paper, are well worth the time to highlight (copy) and watch including building a homemade
cal kit, copper tape microstrip and more.
The PAPER:
A YOU TUBE VIDEO on cal kits and their construction and more...
youtube.com/watch?v=Ws1mIK-JIrg
|
Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
I see another person who asks themselves where did I ever find time to work. Retirement while every day "may" seem like Saturday there are days when it feels more like the first day after after a long weekend and the work is piled so high you can not see any daylight.
"The Golden Years, more like "Fools Gold" at times. "More Work and No Pay."
|
Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
finding anything like that in the dumpster. I am envious. I worked with Lab Grade VNA since 1979 and continued until I retired in 2001. I received a nanoVNA for Christmas 2024.
having a VNA which fits in my pocket and I can take anywhere I choose is amazing. I feel so spoiled now being able to test my antennas with a nanoVNA any time I choose. I can see the results of my calculations come to life one the screen on the VNA. Reminds me of college where the theory we studied in the morning was exercised in live applications in the afternoon.
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Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
Having the 8753C is a privilege of once having worked for HP. As you may
know, HP (before Carly - the wicked witch of the west) encouraged dumpster
dipping. There were two of these in the dumpster. I chose the one with
all the adaptors in place. All the cal kits were also there. So.......
the rest is history. My interests end when one has to involve waveguide.
Dave - W?LEV
toggle quoted message
Show quoted text
On Wed, May 21, 2025 at 12:03?AM Michael Carter <Mike.Carter@...> wrote: Thanks, Dave - the incremental improvements are less critical than the
final result, of course. I need to make up a similar test fixture and
assess its residual coupling with nothing on the alligator clips.
You're fortunate to have the HP 8753C to use at home. Had one at our
university lab, but I use a DG8SAQ VNWA at home, and the university got a
better Agilent VNA with wider frequency coverage beyond 6 GHz if I should
do more microwave work in the future.
73,
Mike, K8CN
------------------------------
*From:* David Eckhardt <davearea51a@...>
*Sent:* Tuesday, May 20, 2025 7:11 PM
*To:* Michael Carter <Mike.Carter@...>
*Cc:* NANO VNA <[email protected]>; Ham-Antennas <
[email protected]>; Ham Antennas <[email protected]>;
Kenneth Wyatt <emc.guru@...>; AA0RS@... <
AA0RS@...>; David Feldman <wb0gaz@...>
*Subject:* Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
CAUTION: This email originated from outside of the University System. Do
not click links or open attachments unless you recognize the sender and
know the content is safe.
I can't give you numbers of improvement as I didn't record those. But I
can give you the order of additions.
1) Lengthened the shield between the ports. It was originally only the
width of the main board. supporting the BNCs.
2) Playing with a thin sheet of double sided board, I added the
additional orthogonal shields. I was going to enclose each port except for
the lond ends, but in "playing" with the essentially scalar network
analyzer, I discovered I gained just as much by shielding opposite sides of
each port.
3) That looked pretty good, but again playing with just a piece of AWG #18
stripped solid copper wire, I discovered the added wires on each side of
the alligator clips really bought me a lot. And, yes, I believe your
analysis that the wires form a transmission line which electrically looks
much like a trough line but allows access to the clips.
4) From there, I could make minor improvements in isolation, but all
those severely limited physical access to the alligator clips. The
additional improvements traded off against physical access was clear I'd
stop where I was. The 70 dB (somewhat +) isolation between ports was quite
satisfactory for me. I could dig deeper into the noise by increasing the
output of the source port on the 8753C, but, again, any additional physical
components would limit access to the clips. So I stopped with what you
see.
Now I gotta wonder how high in frequency it maintains the isolation and
good RF performance. Maybe tomorrow? I have too many projects lined up in
retirement. It's the satisfaction and joy of having good RF test equipment
in retirement!
Dave - W?LEV
On Tue, May 20, 2025 at 8:06?PM Michael Carter <Mike.Carter@...>
wrote:
Hi Dave (W0LEV),
Your measurements of your improved test fixture are impressive. I seem to
recall your original fixture had a single PCB shield between the alligator
clips? Now I'm curious about your thought process as you added bits and
pieces to that original fixture and found improved isolation between the
ports. While I understand adding more PCB walls, the addition of wire
bridges, and particularly the wires paralleling the alligator clips,
intrigues me. My sense is that you have created a transmission line on
each port comprising the alligator clip and its paralleled 'shield' wire,
and the shield wire helps terminate fields and weaken those fringing fields
that couple to the other port. Is this an accurate understanding of your
progression? Do you recall the order in which pieces were added and the
incremental improvement in port isolation you obtained at each step along
the way?
Thanks, and 73,
Mike, K8CN
------------------------------
*From:* [email protected] <[email protected]> on
behalf of W0LEV via groups.io <davearea51a@...>
*Sent:* Tuesday, May 20, 2025 3:38 PM
*To:* NANO VNA <[email protected]>; Ham-Antennas <
[email protected]>; Ham Antennas <[email protected]>
*Cc:* Kenneth Wyatt <emc.guru@...>; AA0RS@... <
AA0RS@...>; David Eckhardt <davearea51a@...>; David Feldman <
wb0gaz@...>
*Subject:* [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
CAUTION: This email originated from outside of the University System. Do
not click links or open attachments unless you recognize the sender and
know the content is safe.
As promised, I made some rigorous measurements of my home brew fixture for
making transmission measurements of various HF circuit elements using a
"professional" instrument. I could have used the NANOVNAs, but using HP
might add some credence to the results ????? Subjects for the fixture
might include common mode chokes, ugly baluns (which I do not use), current
baluns (which I use wound of RG-400 on toroids), filters, and other active
and passive circuits where a fixture is required.
I took the time to calibrate my HP8753C using HP standards with a full
2-port cal from 1 to 30 MHz to make these measurements of the fixture.
Please have a read of the attachment for the results. While the fixture is
essentially free for a few inexpensive components and my time (retired, so
that's free, too). While it's not up to the old HP standards, not bad for
a home baked project which will lead to other projects.
Oh, yes,..... any typos are also free.
If you attempt duplication based on the images, YMMV. Dimensions can be
scoped from the standard alligator clips which are 1.3-inches tip-to-tip (¡À
amateur measurement relying on a non-RF ruler).
Measure everything. Let the data speak for itself, *not *opinion, snake
oil, or sorcery.
Dave - W?LEV
--
*Dave - W?LEV *
-- *Dave - W?LEV*
--
Dave - W?LEV
|
Re: [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
I can't give you numbers of improvement as I didn't record those. But I
can give you the order of additions.
1) Lengthened the shield between the ports. It was originally only the
width of the main board. supporting the BNCs.
2) Playing with a thin sheet of double sided board, I added the additional
orthogonal shields. I was going to enclose each port except for the lond
ends, but in "playing" with the essentially scalar network analyzer, I
discovered I gained just as much by shielding opposite sides of each port.
3) That looked pretty good, but again playing with just a piece of AWG #18
stripped solid copper wire, I discovered the added wires on each side of
the alligator clips really bought me a lot. And, yes, I believe your
analysis that the wires form a transmission line which electrically looks
much like a trough line but allows access to the clips.
4) From there, I could make minor improvements in isolation, but all those
severely limited physical access to the alligator clips. The additional
improvements traded off against physical access was clear I'd stop where I
was. The 70 dB (somewhat +) isolation between ports was quite satisfactory
for me. I could dig deeper into the noise by increasing the output of the
source port on the 8753C, but, again, any additional physical components
would limit access to the clips. So I stopped with what you see.
Now I gotta wonder how high in frequency it maintains the isolation and
good RF performance. Maybe tomorrow? I have too many projects lined up in
retirement. It's the satisfaction and joy of having good RF test equipment
in retirement!
Dave - W?LEV
toggle quoted message
Show quoted text
On Tue, May 20, 2025 at 8:06?PM Michael Carter <Mike.Carter@...> wrote: Hi Dave (W0LEV),
Your measurements of your improved test fixture are impressive. I seem to
recall your original fixture had a single PCB shield between the alligator
clips? Now I'm curious about your thought process as you added bits and
pieces to that original fixture and found improved isolation between the
ports. While I understand adding more PCB walls, the addition of wire
bridges, and particularly the wires paralleling the alligator clips,
intrigues me. My sense is that you have created a transmission line on
each port comprising the alligator clip and its paralleled 'shield' wire,
and the shield wire helps terminate fields and weaken those fringing fields
that couple to the other port. Is this an accurate understanding of your
progression? Do you recall the order in which pieces were added and the
incremental improvement in port isolation you obtained at each step along
the way?
Thanks, and 73,
Mike, K8CN
------------------------------
*From:* [email protected] <[email protected]> on
behalf of W0LEV via groups.io <davearea51a@...>
*Sent:* Tuesday, May 20, 2025 3:38 PM
*To:* NANO VNA <[email protected]>; Ham-Antennas <
[email protected]>; Ham Antennas <[email protected]>
*Cc:* Kenneth Wyatt <emc.guru@...>; AA0RS@... <
AA0RS@...>; David Eckhardt <davearea51a@...>; David Feldman <
wb0gaz@...>
*Subject:* [Ham-Antennas] FIXTURE for XMSN MEASUREMENATS 2.0
CAUTION: This email originated from outside of the University System. Do
not click links or open attachments unless you recognize the sender and
know the content is safe.
As promised, I made some rigorous measurements of my home brew fixture for
making transmission measurements of various HF circuit elements using a
"professional" instrument. I could have used the NANOVNAs, but using HP
might add some credence to the results ????? Subjects for the fixture
might include common mode chokes, ugly baluns (which I do not use), current
baluns (which I use wound of RG-400 on toroids), filters, and other active
and passive circuits where a fixture is required.
I took the time to calibrate my HP8753C using HP standards with a full
2-port cal from 1 to 30 MHz to make these measurements of the fixture.
Please have a read of the attachment for the results. While the fixture is
essentially free for a few inexpensive components and my time (retired, so
that's free, too). While it's not up to the old HP standards, not bad for
a home baked project which will lead to other projects.
Oh, yes,..... any typos are also free.
If you attempt duplication based on the images, YMMV. Dimensions can be
scoped from the standard alligator clips which are 1.3-inches tip-to-tip (¡À
amateur measurement relying on a non-RF ruler).
Measure everything. Let the data speak for itself, *not *opinion, snake
oil, or sorcery.
Dave - W?LEV
-- *Dave - W?LEV*
--
Dave - W?LEV
|
VE6LX
Roger Need
W8NSI James